title: The system uranium-palladium-boron with U(2.5)Pd(20.5)B(6), a new heavy fermion compound.
abstract: Phase equilibria in the system U-Pd-B were established at 850 °C by light optical microscopy (LOM) and x-ray powder and single crystal diffraction. Whereas in as-cast alloys only one ternary compound, τ(1)-U(2 + x)Pd(21 - x)B(6), was found to form at x ∼ 0.5, a further compound τ(2) with hitherto unknown structure was observed in alloys annealed at 850 °C. Due to the formation of suitable single crystals, the crystal structures of two binary compounds, UB(12) and UPd(3) have been redetermined from high precision x-ray data. Similarly, the crystal structure of τ(1)-U(2.5)Pd(20.5)B(6) was investigated by single crystal x-ray diffraction (XRD) revealing isotypism with the Cr(23)C(6)-type, (space group [Formula: see text]; a  = 1.1687(5) nm; R(F)(2)  = Σ|F(0)(2) - F(c)(2)|/ΣF(0)(2) =  0.021). τ(1)-U(2 + x)Pd(21 - x)B(6) is a partially ordered compound where 0.37(1)U + 0.63Pd atoms randomly share the 4a site in (0, 0, 0). Whereas mutual solubility of U-borides and Pd-borides was found at 850 °C to be below 1.0 at.%, a large homogeneity region of fcc-Pd(U, B) extends into the ternary system. U(2.5)Pd(20.5)B(6) has metallic behavior; the ground state properties are determined from a balance of the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, revealing long range antiferromagnetic ordering below 6 K. An extraordinarily large Sommerfeld value (γ > 500 mJ mol(-1) K(-2)) groups U(2.5)Pd(20.5)B(6) among heavy fermion materials.
authors.affiliation: Institute of Physical Chemistry, University of Vienna, A-1090 Wien, Währingerstrasse 42, Austria.
authors.forename: O
authors.initials: O
authors.lastname: Sologub
authors.forename: P
authors.initials: P
authors.lastname: Rogl
authors.forename: E
authors.initials: E
authors.lastname: Bauer
authors.forename: G
authors.initials: G
authors.lastname: Hilscher
authors.forename: H
authors.initials: H
authors.lastname: Michor
authors.forename: E
authors.initials: E
authors.lastname: Royanian
authors.forename: G
authors.initials: G
authors.lastname: Giester
authors.forename: A P
authors.initials: AP
authors.lastname: Goncalves